Trauma depresses natural host defense mechanisms and renders a patient susceptible to infection. While the increased incidence and severity of sepsis in trauma-depressed patients is a leading cause of mortality, the exact nature and extent of the impairment of host resistance has not been fully clarified. Suppression of immune function and particularly of cell-mediated immunity is one of the most consistent failures in the host defenses following trauma. Recent findings in this laboratory indicate that suppressor cell activity is increased in burn-traumatized, immunodepressed animals. This finding may provide an important clue to the causes of immune dysfunction in trauma patients. We propose to study trauma-induced suppressor cells to determine the characteristics and identity of these cells. We also intend to investigate the factors and events related to traumatic injury which contribute to the activation of suppressor cells. Finally, we propose to study the effects of agents known to enhance immune function on trauma-induced immuno-depression in order to determine if these immune defects can be treated therapeutically.